The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head traditionally includes a coil layer embedded in one or more insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic transitions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In current read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
In order to meet the ever increasing demand for improved data rate and data capacity, researchers have recently been focusing their efforts on the development of perpendicular recording systems. A traditional longitudinal recording system, such as one that incorporates the write head described above, stores data as magnetic bits oriented longitudinally along a track in the plane of the surface of the magnetic disk. This longitudinal data bit is recorded by a fringing field that forms between the pair of magnetic poles separated by a write gap.
A perpendicular recording system, by contrast, records data as magnetizations oriented perpendicular to the plane of the magnetic disk. The magnetic disk has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from the write pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer. The resulting magnetic flux then travels through the soft underlayer, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the write pole when it passes back through the magnetically hard top layer on its way back to the return pole.
In order to further increase the performance of a write pole, whether perpendicular or longitudinal, it is necessary to maximize the amount of write field produced by the write coil. The write field can be increased in two ways. First, the amount of write current flowing through the coil can be increased. This however is limited by the amount of heat that can be tolerated as a result of the flow of current through the coil, which, of course, is affected by the resistance of the coil itself. The other way in which the magnetic write field can be increased, is by increasing the number of coil turns passing between the poles of the yoke. This is limited by the space limitations within the yoke.
A traditional process for constructing a coil has involved first depositing an electrically conductive seed layer, and then forming a hard baked photoresist frame over the seed layer. The photoresist layer is constructed with a trench that extends to the seed layer and which defines the coil pattern. After plating the coil, this hard baked photoresist frame must be removed in order to remove the unwanted portions of the seed layer, such as by sputter etching. The seed layer must be removed in order to prevent shorting.
More recently, in longitudinal write head designs a damascene process has been used to construct coils having a higher pitch. The damascene process involves forming a hard baked layer of photoresist, constructing a hard mask over the resist, patterned to define a coil pattern and then removing exposed portions of the hard baked resist to form a coil pattern in the resist. The seed layer is then deposited and the coil is plated. A chemical mechanical polish (CMP) is then used to remove unwanted portions of electrically conductive material deposited over the top of the mask. Because the seed is not deposited beneath the hard baked photoresist layer, this layer can be left intact after the coil has been formed. This allows the coils turns to be formed much closer together.
A feature of hard baked photoresist is that it must be allowed to flow significantly beyond the location where it is needed. In other words the edges of the photoresist layer taper gradually toward the substrate on which the photoresist is deposited. The materials exposed at the air bearing surface (ABS) must be either magnetic pole material or a hard insulating material such as alumina. Hard baked photoresist can not be exposed at the ABS. In a longitudinal head this is not a problem, because the longitudinal write head is formed with a magnetic pedestal that prevents the photoresist layer from flowing to the air bearing surface.
However, in a perpendicular magnetic write head, there is no need for such as magnetic pedestal between the write coil and the ABS. Although some perpendicular write heads have a pedestal in the form of a magnetic shield that extends from the return pole toward the write pole, that pedestal is not necessary and is not included in many designs. In a perpendicular magnetic write head that does not have such a pedestal, there is no structure to provide a dam to prevent a photoresist insulation layer from flowing to the ABS. In that case, the space between the coil and the ABS is usually filled with a hard, non-magnetic, insulating material such as alumina. This alumina layer is deposited after the formation of the coil. A hard material such as alumina is needed at the ABS, to provide sufficient protection against corrosion, abrasion, etc. As mentioned above, a hard baked photoresist insulation layer cannot be allowed to extend to the ABS. Because of this, only more traditional coil formation processes (where the resist is completely removed after coil formation) have been used in perpendicular write heads having no pedestal structure. The advantages of using damascene coil formation processes have, therefore, not been available in the construction of such perpendicular write heads.
Therefore, there is a strong felt need for a write pole design that can allow a high pitch coil to be constructed in a perpendicular write head having no pedestal. Such as design must be easily manufacturable, using processes that will not add significant cost or complexity to the head construction.